The invention is directed to a material for electrical contacts or switches made of silver, tin oxide (SnO.sub.2) and a further metal oxide and process for producing it.
For the production of electrical contacts or switches there has previously proven best for a large number of uses Ag/CdO. Because CdO pollutes the environment, however, there have been intensified searches to replace CdO by another metal oxide. In these investigations it has been found that SnO.sub.2 is a suitable replacement for CdO. Because of the higher thermal stability of SnO.sub.2 compared to CdO there results a clearly reduced rate of consumption which leads to a longer life. However, a very substantial disadvantage of Ag/SnO.sub.2 is that the contact resistance at the switch after several thousand switchings is too high through formation of a coating layer. As a rule this leads then to increased temperatures in the switching device, which can lead to the destruction of the device and therefore are inadmissible.
A further disadvantage of this Ag/SnO.sub.2 material compared to Ag/CdO is the lower safety against welding. The forces which are required to tear apart the welding bridge are in part twice as high as with Ag/CdO switches. Therewith there are the changes of switching disturbances with insertion of Ag/SnO.sub.2.
Therefore have been attempts to increase the welding safety by the addition of further metal oxides to Ag/SnO.sub.2 in which case there are used, for example, bismuth oxide (German O.S. No. 2754335) or indium oxide (Gemeran O.S. No. 2428147). Indeed these additives improve the welding safety but are accompanied, however, by an increased temperature at the contact and at the switching device which impairs the life of the device.